1. Field of the Invention
The present invention relates to a novel method for preparing a (meth)acrylic ester-based graft copolymer having a regulated molecular structure.
2. Description of the Prior Art
For the purpose of improving the function and performance of polymeric materials, block copolymers and graft copolymers have been heretofore developed. In recent years, the synthetic techniques of oligomers and polymers (macromonomers) each having a polymerizable functional group at the terminal thereof have been advanced, and much attention is paid to the development and application of the graft copolymers by the use of these techniques. As the synthetic techniques of the macromonomers, various methods have been suggested so far. For example, there have been a Milkovich et al's anion polymerization method (Japanese Patent Laid-open Nos. 21486/1972, 116586/1975 and the like), a radical polymerization method of ICI Ltd. (Japanese Patent Laid-open Nos. 11224/1968 and 16147/1968), a radical polymerization method of Du Pont (U.S. Pat. No. 3,689,593) and a GTP (group transfer polymerization) method of Toagosei Chemical Industry Co., Ltd. (Japanese Patent Laid-open No. 62801/1987). However, the above-mentioned anion polymerization method has the drawback that it is difficult to apply the same method to (meth)acrylic ester monomer. In the above-mentioned radical polymerization method, the obtained macromonomer contains bifunctional components attributed to a side reaction such as the termination of recombination, and when this method is used to manufacture the graft copolymer, a crosslinking reaction occurs and the obtained graft copolymer inconveniently has poor moldability. The above-mentioned GTP method is suitable for the synthesis of the macromonomer by the use of a (meth)acrylic ester and can provide the macromonomer having a high purity, and so it is more excellent than the other methods in these points. However, the synthetic reaction of an initiator which is used in the preparation of the macromonomer is a multi-stage reaction, so that yield is low (about 10 to 20%). In consequence, the GTP method is not considered to be a satisfactory industrial production method. Furthermore, in the case of the GTP method, the composition of the graft copolymer is often distributed in a certain range, depending upon a copolymerization reactivity ratio between the polymerizable vinyl group of the macromonomer and a comonomer, and it is not easy to obtain the graft copolymer having a regulated structure. Moreover, in the polymerization of the macromonomer and the comonomer, the solubility of the macromonomer in the comonomer is often low, and in a solution radical polymerization which is often used, there is the problem that it is difficult to increase the molecular weight of a backbone polymer. As understood from the foregoing, these conventional graft copolymer preparation methods using the macromonomer are not suitable for the formation of the graft copolymer having the regulated molecular structure in compliance with a molecular design.
On the other hand, the above-described GTP method has been proposed as a method for preparing methyacrylic resins or copolymer thereof by Du Pont in U.S. Pat. Nos. 4,414,372; 4,417,034; 4,508,880; 4,524,196 and the like. However, these patents disclose methods for preparing the above-described macromonomer or a block copolymer but do not disclose a method for preparing a graft copolymer.